1. Field of Invention
The present invention relates to a time correction device for setting the time based on a signal from a positioning satellite such as a GPS satellite, to a timepiece having the time correction device, and to a method of correcting the time.
2. Description of the Related Art
The Global Position System (GPS), which is a system enabling a receiving device to determine its own position, uses satellites (GPS satellites) that each orbit the Earth on a specific path. Each GPS satellite has an on-board atomic clock and keeps time with extremely high precision.
Japanese Patent No. 3512068 (JP2001-59864) (paragraph [0001]) teaches a method of using data from the atomic clock of a GPS satellite to correct the time kept by a timepiece with high precision.
In order to get the time from the atomic clock of a GPS satellite, however, the GPS receiver must capture a GPS satellite and synchronize with the GPS satellite signal.
The GPS satellites are also constantly moving, and the approximate positions of the GPS satellites must be estimated from orbital information about the GPS satellites in order to capture a satellite.
Yet further, at least four GPS satellites must be captured in order to acquire precise time information.
In addition to capturing four moving GPS satellites being time-consuming, if the GPS receiver is built into a device such as a timepiece that also moves with the user, capturing a GPS satellite is even more difficult because the receiver is moving, and capturing four GPS satellites takes a long time.
This means that much time and power are consumed capturing the GPS satellites, and incorporating a GPS receiver into a device such as a timepiece that has a very small power supply is difficult. As a result, correcting the time kept by a timepiece with high precision is in practice not possible using GPS signals.